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UNIT #6 “ BASIC ELECTRICITY AND POWER SUPPLIES”
I.
II.
III.
Electrical power
A. Negative electrons flow to positive
B. Current flows in a closed system
C. Current does not flow in an open system
Electrical terms
A. Voltage
1. The force of electricity in a system
2. Voltage is measured as the difference between the charge on one
side of the device from the other.
3. A voltmeter/multi-meter measures the current
B. Amps
1. The volume of electrons that flow through a point at a given time
2. An ammeter/multi-meter measures the volume of electrical
currents
3. There is a direct relationship between volts and amps
C. Ohms
1. Resistance is the property that opposes flow of electricity
2. Continuity is the opposite of resistance
3. Resistors are used to regulate flow of electricity
4. Resistance is measured in Ohms
5. Ohm’s law states “As resistance decreases, either current or
voltage increases.
D. Wattage
1. Wattage is the total amount of power needed to operate an
electrical device
2. The number of watts is calculated by multiplying volts times
amps. 120 volts x 5 amps = 600 watts
AC/DC
A. AC – alternating current
1. Oscillates back and forth rather than traveling in one direction
2. In US household current is 110-120 volts at 60 Hz (60x per min.)
3. Increased voltage and decreased current amps causes electricity
to travel great distances
4. Decreased voltage and increased amps helps power household
appliances
B. DC – direct current
1. Current moves only in a straight line
2. Is the type of current used in PC’s
3. A transformer changes the ratio of current to volts
4. A rectifier changes AC to DC
IV.
5. Power supplies on a computer are both transformers and
rectifiers. They change current from AC to DC and volts from
110 to +/- 12, 5, & 3.3 volts
C. Hot, Neutral, and Ground
1. Electricity flows from the power plant to the home appliance
through the hot wire and is returned to the power plant through
the neutral wire. If shorts exist the ground dissipates the charge
2. Short circuits happen when uncontrolled electricity flows from
hot to neutral or ground.
3. Electrons always seek the path of least resistance
4. Never become the path of least resistance
5. Fuses protect against increased flow of electricity and are rated
in amps.
6. In 110 AC black is hot, neutral is white, and ground is green or
bare.
7. In 220 block or read are hot, white is neutral, and green or bare
are ground.
8. The neutral line is grounded several times.
a. Power company equipment
b. Utility poles
c. Switch boxes
d. Electrical outlets in the home
9. PC components must be grounded. Never use a two prong plug.
D. Components
1. Conductor – allows electricity to pass through it
2. Insulator – does not allow electricity to pass through it
3. Semi-conductor – allows electricity to pass through it to some
degree
4. Transistor – allows connectivity or not as a plus or a minus and
can store the logic setting to conserve energy
5. Capacitor – can store an electrical charge for an extended period
of time. Can create smooth electrical flow
6. Diode – allows electricity to flow in one direction. Transistors
have an number of built in diodes
Protecting Your System
A. Make notes about any repairs or electrical problems
B. Remove packing tape and cellophane from work area ASAP
C. Keep components away from hair and clothing
D. Keep screws in a cup or tray
E. Don’t stack circuit boards on top of each other
F. Don’t touch chips on circuit boards
G. Don’t touch chips with a magnetized screwdriver
H. Don’t’ use a graphite pencil to change dip switches
I. Double check your work before you turn on the computer
J. Turn off the computer before moving it
K. Protect disk from magnets, heat, jarring, etc.
V.
Protect Yourself
A. Don’t touch anything inside the computer case while the computer is
plugged in.
B. Treat the power supply like a “black box”. Never remove the cover and
touch anything inside
C. Monitors and power supplies contain capacitors with enough stored
electricity to kill you.
VI.
ESD
A. ESD is Electrostatic Discharge
B. It can destroy entire circuit boards
C. It is made up of free electrons
D. Wrist straps or frequently grounding yourself will protect your equipment
E. Do not wear wrist straps when working on a monitor or inside a power
supply case
F. Use anti-static bags for circuit boards
VII.
EMI
A. EMI is electromagnetic interference
B. Electrons can escape from electrical lines and devices
C. EMI can disrupt operation of a component
D. RFI is when EMI is on the same frequency range as a radio. It stands for
radio frequency interference
E. Power supplies are shielded to avoid this
F. Moving a computer can eliminate this problem
G. Keep network cables away from any electrical lines, motors, or
components.
Surge Protection and Battery Backup
A. Surge Protectors protect against spikes and are rated in joules
B. Uninterrupted Power Supplies protect against brownouts and blackouts
C. Data line protection does the same things for phone and network
connection as a UPS for electrical appliance
D. UPS’ can also protect against spikes and provide power during blackouts.
VIII.
IX.
Energy Conservation
A. Green star equipment meets EPA standards for low electrical use
B. Many devices use some sort of power management
1. APM – Advanced power management – used by Intell and
Microsoft
2. AT attachment or ATA - provides for less energy for EIDE
drives.
3. DPMS – Display Power Management Signaling provides
conservation for monitors
4. ACPI – Advanced Configuration and Power Interface is a system
used by Windows 98, 200 and XP. It controls power use
including sleep and hibernation mode.